Field of Invention
The present invention relates to a power management circuit, and a control circuit and a control method thereof; particularly, it relates to such power management circuit, and control circuit and control method thereof, which are capable of adjusting the output voltage according to a power supplying capability of the input terminal to improve the power supply efficiency.
Description of Related Art
Please refer to FIG. 1A in conjugation with FIG. 1B. FIG. 1A shows a schematic diagram of a conventional power management circuit. FIG. 1B shows an embodiment of the first operation circuit of the prior art. The power management circuit 10 is capable of converting an input voltage VIN at an input terminal IN to an output voltage VSYS at an output terminal SYS and charging a battery BAT from the output terminal SYS. The input terminal IN can be coupled to an external power source 18 to receive power supply from the external power source 18, so that an input current Iin is supplied from the input terminal IN. The output terminal SYS can be coupled to a load 19 to provide the output voltage VSYS to the load 19 from the output terminal SYS. As shown in FIG. 1A, the power management circuit 10 comprises a first linear regulator 11 and a second linear regulator 12. The first linear regulator 11 and the second linear regulator 12 for example are low-dropout regulators (LDO), respectively. The first linear regulator 11 includes a first switch 111 and a first operation circuit 112. The first operation circuit 112 generates a first operation signal S1′ which controls an operation of the first switch 111. As shown in FIG. 1B, the first operation circuit 112 includes an error amplifier EA1′. The error amplifier EA1′ compares a feedback signal (representing information related to the output voltage VSYS) with a reference voltage REF to generate the first operation signal S1′, thus controlling the operation of the first switch 111 so that the first switch 111 is conductive and operates in its linear region. The power management circuit 10 can optionally comprise a first voltage detection device 16. The first voltage detection device 16 can be, for example, a voltage divider circuit which generates the feedback signal FB1′ representing information related to the output voltage VSYS. The second linear regulator 12 having one end electrically connected to the output terminal SYS and another end electrically connected to the battery BAT. The second linear regulator 12 includes a second switch 121 and a second operation circuit 122, wherein the second switch 121 is electrically connected between the output terminal SYS and the battery BAT. When the input terminal IN receives power supplied from the external power source 18, the power supplied from the external power source 18 can support a charging current ICHG from the output terminal SYS to the battery BAT, to charge the battery BAT. Under such circumstance, the second operation circuit 122 generates a second operation signal S2′ according to a feedback signal FB2′ (representing information related to a battery voltage VBAT of the battery BAT) and a feedback signal FB3′ (representing information related to the charging current ICHG flowing through the second switch 121), to control an operation of the second switch 121 so that the second switch 121 is conductive and operates in its linear region, thereby controlling the charging operation from the output terminal SYS to the battery BAT. The power management circuit 10 can optionally comprise a second voltage detection device 17. The second voltage detection device 17 can be, for example, a voltage divider circuit which generates the feedback signal FB2′ representing information related to the battery voltage VBAT of the battery BAT.
In this prior art, the reference voltage REF shown in FIG. 1B is a constant and cannot be adjusted. Therefore, the level or regulated target of the output voltage VSYS is correspondingly a constant and cannot be adjusted. Because both the first linear regulator 11 and the second linear regulator 12 are linear regulators and the first switch 111 and the second switch 121 both operate in the linear region, there is a dilemma in determining the level of the output voltage VSYS. That is, when the level or regulated target of the output voltage VSYS is set closer to the level of the battery voltage VBAT, the power loss from the output terminal SYS to the battery BAT is lower but the power loss from the input terminal IN to the output terminal SYS is higher. On the contrary, when the level or regulated target of the output voltage VSYS is set closer to the level of the input voltage VIN, power loss from the input terminal IN to the output terminal SYS is lower but the power loss from the output terminal SYS to the battery BAT is higher. As a consequence, in the prior art, regardless whether the level of the output voltage VSYS is set closer to the level of the battery voltage VBAT or closer to the level of the input voltage VIN, there will be undesirable power loss.
In view of the above, to overcome the drawback in the prior art, the present invention proposes a power management circuit, and a control circuit and a control method thereof, which are capable of adjusting the output voltage according to a power supplying capability of the input terminal to improve the power supply efficiency.